Fermentation processes generally produce end products that typically need to be separated and recovered for further use. In fermentation processes that incorporate the use of a microorganism that can ferment a carbon source to form an acid type product, it is often difficult to get the desired end product at a sufficiently desirable concentration and in a form that is reasonably efficient to separate and recover.
Rhodes, R A, Lagoda, A A, Misenheimer, T J, Smith, M L, Anderson, R F, and Jackson, R W, Production of Fumaric Acid in 20-Liter Fermentors, Appl Microbiol 10:9-15 (1962), describe some of the problems associated with producing a particular organic acid, fumaric acid. The Rhodes article discloses a variety of fermentation methods in which glucose was fermented with Rhizopus arrhizus to produce fumaric acid. The fermentations were carried out so as to form calcium, sodium and potassium salts of the acid. Calcium fumarate was produced at a significantly higher concentration compared to the sodium and potassium salt forms. The calcium salt form was found to be insoluble and to lead to a thixotropic broth. The sodium and potassium salt forms were found to be soluble, but the fermentation was inhibited when the concentration of fumarate salts reached 3.5 to 4.0%.
U.S. Pat. No. 4,877,731, discloses a fermentation process for producing carboxylic acids. The process includes growing fungi of the genus Rhizopus in a culture medium containing a carbon source, a nitrogen source and inorganic salts, under conditions of controlled oxygen availability wherein the dissolved oxygen concentration for the cell growth phase is between 80% and 100% and where the dissolved oxygen concentration for the acid production phase is between 30% and 80%. To realize the benefit of the invention, it is necessary to add calcium carbonate to the culture medium.
It would be desirable to find alternative or additional methods of producing organic acids at relatively high acid concentrations. It would be further desirable to produce organic acids using a process in which it is relatively easy to separate and recover the desired acid component.